The active materials in a battery contain rare metal components, such as cobalt, nickel, manganese, and lithium. A compound including any of the rare metal components as a main component is particularly used for the positive electrode active material of a non-aqueous electrolyte secondary battery. In order to preserve resources for such a rare metal component, there is a need for a method for recovering a rare metal component from a waste battery material of a secondary battery.
As a conventionally proposed method for recovering rare metal components from a waste battery material and reusing the same, there is a method in which an electrode composed of a current collector and an electrode material mixture, or the electrode material mixture peeled from the current collector is immersed in a solution to dissolve rare metal components to extract the rare metal components into the solution, and then, the resulting solution is filtered to remove insoluble components and the pH of the rare metal component-containing solution is adjusted, whereby rare metal hydroxides and carbonates are precipitated and recovered, resulting in the recovery of raw materials for an active material (for example, see Patent Literature 1).
The hydroxides, carbonates, and chlorides of rare metal components recovered by the method are reused again as raw materials for an active material.
However, the dissolution and precipitation of rare metal components require a solution capable of dissolving the rare metal components and additionally a chemical agent for precipitating the components. In addition, it is industrially difficult to precipitate lithium that is highly soluble in aqueous solutions. Furthermore, when pH adjustment is made by adding a chemical agent including other alkali metal elements such as sodium and potassium in order to precipitate the transition metal component, it is industrially substantially difficult to separate the alkali metal elements and lithium from each other. Therefore, isolation of lithium for recovery is substantially difficult in industrial areas.
Furthermore, since waste liquids of the used solution and chemical agent are produced, disposal thereof becomes necessary. Additionally, in order to reuse, as an active material, the raw materials of an active material recovered, it is necessary to perform, in addition to a step of recovering the raw materials of the active material from a waste battery material, a step of producing an active material from the raw materials of the active material. Accordingly, manufacturing cost and manufacturing energy are needed to produce the active material from the raw materials of the active material, thus resulting in a problem from the viewpoint of economical efficiency and energy saving.
On the other hand, there is a proposed method for recovering an active material directly from a waste battery material without going through the step of producing an active material from the raw materials of an active material.
For example, Patent Literature 2 discloses a method in which an electrode is immersed in a solvent of N-methyl-2-pyrrolidone (hereinafter may be referred to as NMP), an NMP-containing mixed solvent, or the like as a solvent serving to dissolve only a binder among an active material, a conductive material, and the binder that constitute the electrode, whereby the binder is dissolved in the solvent to separate and recover a mixture product of the active material and the conductive material from the current collector, and then, the mixture product is calcined to burn the conductive material so as to recover the active material, thereby reusing the active material as an active material of a secondary battery again.
Instead of dissolving the active material to reuse as a solution containing each constituent element, directly recovering the active material and allowing the reuse thereof do not need manufacturing cost and manufacturing energy taken to produce an active material from raw materials of the active material, since it is the direct recovery of active material, and thus is more advantageous than the conventionally proposed method for recovering raw materials of an active material from a waste battery material and producing an active material from the raw materials of the active material for reuse thereof.
However, the method of Patent Literature 2 for recovering an active material from a waste battery material for reuse thereof requires an organic solvent for immersing the electrode to dissolve the binder, as well as requires liquid waste disposal for the used organic solvent.